Tools incorporating fluid-filled impulse units are known in the art; for example, a fluid pressure impulse nutrunner is disclosed in U.S. Pat. No. 4,836,296 to Biek. Some of the impulse units have included automatic shut-off devices, but these impulse units and shut-off devices have had numerous shortcomings.
One shortcoming may be that the impulse tool begins the shut-off process too early. For example, the tool may begin shut-off as the pulsing begins, which for a nutrunner or torque wrench frequently occurs after the initial phase of running the nut down loose threads. Other shut-off devices may cause the impulse unit to shut-off after a single blow of significant magnitude that may be in error because of complex inertial effects associated with the torsional drive train (spindle, socket, fastener, etc.). Similarly, the shut-off may be unreliable because of sensitivity to transient high pressure shock waves or pressure peaks that occur within liquid-filled impulse units during acceleration of initially non-rotating or slowly rotating components. Other shortcomings may include oil leakage, clogging of small orifices in the device, inadequate heat transfer away from the tool or device, high vibration, large size, and high noise levels. Further shortcomings may exist as these are but a few examples.
Therefore, a need has arisen for an improved impulse tool and improved shut-off device that will not shut off prematurely, that reduces oil leakage, that reduces vibration, that provides enhanced cooling, or that is capable of smaller sizing.